This invention relates to an improved apparatus and method of preventing cold working of slip assembly components, and more particularly, to an apparatus and method of applying a material to a contact surface of a slip segment or a slip bowl, to prevent cold working between the slip segment and the slip bowl.
When drilling for oil or gas, a platform is typically used to support a circular rotary table. Rotational energy is supplied to the rotary table through motors or the like, to move the rotary table in a circular fashion. The rotary table includes a central kelly bushing which provides a central opening or bore through which a drill pipe or a drill string passes. The kelly bushing typically includes four xe2x80x9cpin holesxe2x80x9d which receive pins on the master bushing that drives the kelly when interlocked with the kelly bushing. The rotary table, kelly, master bushing and kelly bushing are art terms which refer to the various parts of the drilling rig which impart the needed rotational force to the drill string to effect drilling. Such well drilling equipment is known in the art.
When adding or removing a drill pipe from the drill string, wedges, commonly referred to as xe2x80x9cslipsxe2x80x9d are inserted into the rotary table central opening to engage a slip bowl. The slips wedge against the drill pipe to prevent the pipe from falling into the well bore. Often, placement of the slips is manual, and slips or slip assemblies (assemblies of a plurality of slips linked together) usually include handles for gripping and lifting by well personnel, commonly referred to as xe2x80x9croughnecksxe2x80x9d. Typically, rigs are equipped with such xe2x80x9chand slipsxe2x80x9d. When a pipe is disconnected from the drill string, using a power tong or the like, the remaining portion of the drill string can be supported so that additional sections of pipe can be added to/or removed from the drill string.
A more modern and commonly used slip system, called a xe2x80x9cpower slipxe2x80x9d, includes a plurality of slip segments or slip assemblies that are retained within a slip bowl to prohibit the slips from vertical movement while the slip bowl rotates with the rotary table about the drill pipe. The slips and the bowl are configured such that outer surfaces of the slip segments contact inner surfaces of the slip bowl with sliding friction.
A problem commonly experienced by these power slip systems is that the sliding friction between the slips and the bowl tend to cause these parts to stick or seize upon rotation of the bowl about the slip. Since both the slips and the bowl are generally made from steel, the two parts, when loaded together at a combination of high contact pressure and high sliding friction, have a tendency to bond together in a process called cold welding. The more alike the atomic/elemental structures of both the parts are, the higher the probability that the parts will cold weld. Such cold welding can be catastrophic because the seized parts will tend to rotate the drill pipe with the rotary table and make disengagement of a drill pipe from the drill string improbable.
One method commonly used for reducing cold working between the slip and the slip bowl is to lubricate the parts with a lubricant, such as grease. However, this method requires that the parts be lubricated/greased frequently, typically every 20 to 30 cycles, which can be expensive and harmful to the environment.
Accordingly, there is a need for an inexpensive and environmentally safe method of treating the contact surfaces of the slips segments or the slip bowl, such that cold working between the slip segments and the slip bowl is reduced.
The present invention is directed to an oil or gas well slip system having a slip bowl with an interactive contact surface and a slip assembly having a mating interactive contact surface for slidable engagement with the slip bowl interactive contact surface, wherein the slip bowl and the slip assembly are each comprised of a first material. A second material is attached to the interactive contact surface of either the slip bowl or the slip assembly, wherein the second material is compositionally different from the first material to prevent cold welding between the slip bowl and the slip assembly, and wherein the second material has little or no tendency to dissolve into the atomic structure of the first material.
Another embodiment of the invention is directed to a method of reducing cold welding between a slip assembly and slip bowl of an oil or gas well slip system. The method includes providing a slip having an interactive contact surface, providing a slip assembly having a mating interactive contact surface for slidable engagement with the slip bowl interactive contact surface, wherein the slip bowl and the slip assembly are each formed from a first material, and attaching a second material to the interactive contact surface of either the slip bowl or the slip assembly, wherein the second material is compositionally different from the first material to prevent cold welding between the slip bowl and the slip assembly and wherein the second material has little or no tendency to dissolve into the atomic structure of the first material.